1. Field of the Invention
The present invention relates to active as well as passive sensor systems. More specifically, the present invention relates to method and apparatus for processing data provided by such systems.
While the present invention is described herein with reference to an illustrative embodiment for a particular application, the invention is not limited thereto. Those of ordinary skill in the art having access to the teachings provided herein will recognize additional modifications, applications, and embodiments within the scope thereof.
2. Description of the Related Art
Conventional sensing systems typically include semiconductor detection devices which provide hundreds of thousands of individual picture elements or pixels. The collection of pixels may be provided by a two-dimensional focal plane of a staring sensor or by a one-dimensional line of detectors of a scanning sensor.
Each pixel is essentially a signal received by the sensor for a particular point in the filled of view thereof. Conventional processing involves operations on the received signals to improve the quality of a resulting composite image. That is, the signal for each pixel is typically processed to improve the signal-to-noise ratio (SNR) and thereby enhance the quality of the detected image. In many systems, at each point in a scene, signals from neighboring pixels are convolved with a matched filter related to the system defined blur function. This provides a corrected signal value for the point which is used for image enhancement. This filtering process is applied to each point in the scene until the entire scene has been filtered, whereupon, the process is repeated.
Current technology for producing such arrays provides pixel sizes smaller than the typical blur spot created by the imaging optics of the sensor. Accordingly, conventional filtering procedures are time consuming and require substantial processing. Thus, there is a recognized need in the art to improve the processing efficiency of active and passive image processing systems.
One area of potential improvement is in the spatial or pixel sampling lattice. Current systems use a rectangular (or square) lattice. It has been shown that for a circular blur function, a rectangular sampling lattice is less efficient than a hexagonal lattice of pixels or detector elements. For example, Peterson and Middleton show that for signal reconstruction the most efficient lattice, i.e., the lattice with the minimum number of sampling points to achieve an exact reproduction of a circular wave-number-limited function is hexagonal and not rectangular. See "Sampling and Reconstruction of Wave-Number-Limited Functions in N-Dimensional Euclidean Spaces", by D. P. Peterson and D. Middleton, Information and Control, vol. 5, 1962, pp. 279-323. See also, "Resolution, Signal-to-Noise Ratio, and Measurement Precision", by D. L. Fried, J. Opt. Soc. Am., vol. 69, No. 3, March 1979, pp. 399-406 and "The Processing of Hexagonally Sampled Two-Dimensional Signals", by R. M. Mersereau, Proceedings of the IEEE, vol. 67, June 1979, pp. 930-949.
While these references discuss the theory of hexagonal sampling, there remains a need in the art for a method and apparatus for generating a hexagonal sampling lattice and for using it for active and passive detection with a scanning sensor.